In the current integrated circuit (IC) business, whose total world market is in excess of $60 billion, all of the ICs are manufactured using a 2-dimensional (2-D) technology. This means that all of the IC chips on a single crystal silicon (Si) wafer uses various types of transistors and diodes laid out on the Si surface in a 2-D manner. In such a manufacturing technology, single crystal layers having the same orientation as the Si wafer, known as epitaxial layers are grown on the Si wafer substrate.
This invention relates to the growth of single crystals on amorphous and non-crystal surfaces. The most widely used processes for growing epitaxial layers of Si are chemical vapor deposition (CVD) processes. They use chemicals/gases such as SiCl.sub.4, SiHCl.sub.3 and SiH.sub.2 Cl.sub.2 with H.sub.2 as the carrier and reduction gas in a CVD reactor, at temperatures in the range of 950-1100.degree. C. This is well known, and such CVD processes for the epitaxial grown or deposition of single crystal layers of Si are widely used in IC manufacturing.
Typical chemical reactions which take place, as an example, in the H.sub.2 reduction of SiCl.sub.4 are given below: ##STR1##
The single crystal quality of the epitaxial Si film depends on several factors, such as the crystal perfection of the regions of the single crystal Si substrate, its cleanliness, the rate of deposition of the Si film, and the purity of the gases. These criteria are known to those conversant in the state of the art. However, these processes are limited to growing or depositing epitaxial Si films on single crystal Si substrates (homoepitaxy) which can be used only to manufacture 2-D ICs.
Homoepitaxy processes to grow single crystal films of compound semiconductors, such as gallium arsenide (GaAs), similar to those described above, are available and used for manufacturing compound semiconductor ICs. These are also limited to manufacturing only 2-D compound semiconductor ICs. As an example, GaAs ICs using Schottky technology are dominant for monolithic microwave ICs (MMICs). The CVD, liquid phase epitaxial (LPE) and molecular beam epitaxial (MBE) processes obviously use Ga, As, and their compounds in the appropriate processes. These are also well known to those conversant in the state of the art. The total business volume of 2-D compound semiconductor ICs is much smaller than that of the 2-D Si ICs. Nevertheless, because of the unique performance capabilities of the compound semiconductor devices and ICs for optical (lasers and detectors) and microwave applications, they are very important.
The level of integration in Si Ics, in terms of device density, can be increased beyond the 2-D limit by invoking device fabrication in the third dimension, i.e. by manufacturing 3-D ICs. This would enhance the functionality and the performance of Si ICs beyond the limits of the current 2-D technologies. However, to accomplish this, single crystal Si layers need to be grown over the silicon dioxide (SiO.sub.2) layers used in the 2-D ICs. No production worthy technology is available yet to do this. One of the approaches is to use epitaxial lateral overgrowth (ELO) technology, in which seeding from the substrate is used to grow (epitaxial Si layers over SiO.sub.2 layers (Ref. 1: M. S. Liu and B. Hoefflinger, "Three-Dimensional CMOS Using Selective Epitaxial Growth", U.S. Pat. No. 4,686,758, Aug. 18, 1987). Another approach is to bond two single crystal Si wafers with an SiO.sub.2 layer in between the two.
It is also of interest to grow single crystal Si layers on the single crystal compound semiconductor such as GaAs. This feature of growing two dissimilar single crystal material, one on top of the other, is known as heteroepitaxy. Combining the best of both the worlds of Si and compound semiconductor ICs leads to ultra performance ICs (UPICs) which are the ultimate in the ICs known to mankind (Ref. 2: A. N. Saxena et al., "Technology and Reliability Issues of Multilevel Interconnects in Bipolar, BiCMOS and CMOS VLSIC/ULSIC", Proc. IEEE Bipolar/BiCMOS Circuits and Technology Meeting (BCTM), pp. 12-19, 1993). Thus, the maximum functionality, reliability and low power of Si ICs can be integrated monolithically with the unique performance (optical and microwave) capabilities of compound semiconductor ICs to produce UPICS. No production worthy technology to grow the heteroepitaxy layers is available so far.